The present invention relates to a circular knitting machine and, more particularly, to a takedown unit for drawing down tubular fabric that hangs downwardly in the knitting machine.
A circular knitting machine includes a rotating knitting cylinder with a knitting assembly for forming the tubular knitted fabric. The knitted fabric is delivered from the needles in a hanging condition from the knitting cylinder and rotates with the cylinder. A takedown unit is positioned beneath the knitting cylinder to draw the knitted fabric from the cylinder.
One type of conventional takedown unit rotates synchronously with the knitting cylinder to avoid twisting the fabric as it rotates with the cylinder. This takedown unit includes a pair of elongate, driven pinch rollers. The knitted fabric is fed through the nip defined between the pinch rollers so that the takedown unit flattens the fabric. Problems occur, however, because different portions of the fabric may be exposed to different amounts of pressure and tension, which can cause an undesirable lack of uniformity and other defects in the fabric.
U.S. Pat. No. 6,029,478 to Panuccio discloses a rotating cam box knitting machine with a large number of tensioning rollers that are respectively arranged on stationary axes around the perimeter of the knitted fabric descending from the knitting cylinder. The tensioning rollers cooperate with contrast rollers located on the inside of the knitted fabric, and each tensioning roller is actuated by a separate motor. The tensioning rollers and corresponding freely-rotating contrast rollers avoid problems encountered with pinch rollers that flatten the fabric.
Even though a wide variety of improved takedown units have been developed, it is still common for takedown units to complicate the operation of, or be responsible for problems that occur during the operation of, circular knitting machines. For example, conventional takedown units can introduce defects and distortion in the knitted pile fabric, such as by pinching and thereby marking fabrics made with fragile polymer fibers and yas such as polypropylene or lycra. In addition, in some takedown units, pinched points, folds, and slippage mark defects can be caused by the use of pinch rollers and the pressure between the pinch rollers as the fabric passes through them. Although accurate control of the tension applied to the fabric is fundamental to maintaining high fabric quality, some conventional takedown units fail to provide accurate control. Other takedown units provide accurate control only by incorporating equipment that is unnecessarily cost prohibitive or complicated.
In view of the foregoing and for other reasons, there is a need for an improved takedown unit.
On aspect of the present invention is an improved takedown unit and associated methods used in a circular knitting machine. The takedown unit of the present invention can be characterized as an item that is separate from any circular knitting machine (i.e., a subcombination), in which case the takedown unit may be retrofittable to an existing circular knitting machine. The takedown unit of the present invention can also be in combination with a knitting machine.
One aspect of the present invention is a takedown unit for a circular knitting machine that includes a rotating knitting cylinder for forming tubular fabric such that the tubular fabric hangs downward along a fabric travel path from the knitting needles, with the takedown unit including a set of driven takedown rollers mounted around the fabric travel path, and a floating guide mechanism within/encircled by the hanging tubular fabric and interacting with the takedown rollers. The guide mechanism spreads the hanging tubular fabric for facilitating engagement of the driven takedown rollers against the tubular fabric. Very generally described, the guide mechanism can be in the shape of an inverted top hat, a cone, a truncated cone or a funnel, or the like. The guide mechanism is preferably not rigidly connected to any structure of the circular knitting machine, or the like, so that the guide mechanism floats within the interior of the tubular fabric that is traveling downward from the knitting cylinder. This floating preferably equalizes the forces applied to the fabric by the takedown unit to promote optimal operation. The guide mechanism cooperates with the takedown rollers to define a set of nips through which the tubular fabric extend, and the nips are preferably positioned above the rotational axes of the takedown rollers.
In accordance with one aspect of the present invention, the takedown unit includes a set of cams that extends at least partially around the fabric travel path and cooperates with at least one actuator for driving at least one of the takedown rollers. The cams and takedown rollers are mounted to allow relative rotation therebetween, with this relative rotation being around the fabric travel path. The actuator is positioned for engaging the cams in response to the relative rotation between the takedown rollers and cams, so that the cams preferably actuate the actuator multiple times for each 360 degrees of relative rotation between the set of takedown rollers and the set of cams. Each actuation of the actuator includes a reciprocating motion of a component of the actuator, with the reciprocating motion preferably being upright, although the reciprocating may be radial or in other directions. The actuator is preferably operative for translating the reciprocating motion into unidirectional rotation of at least one of the takedown rollers, with this rotation being for drawing down the fabric.
In accordance with one aspect of the present invention, there is a separate actuator for each of the takedown rollers. In accordance with this aspect, each actuator includes a lever and an output shaft that is preferably configured for rotating substantially only in one direction in response to reciprocation of the lever. The output shaft of each actuator is connected to a respective takedown roller for causing it to rotate preferably substantially only in the one direction and thereby draw down the fabric. Preferably the cams and actuators are operative so that the actuators operate synchronously to rotate the takedown rollers synchronously.
In accordance with one aspect of the present invention, the throws of the cams are adjustable for the purpose of adjusting the action of the actuators and thereby the rotation of the takedown rollers. In accordance with this aspect, an adjustment ring preferably extends around the series of cams, with the adjustment ring and the series of cams being mounted to allow relative rotation therebetween, with this relative rotation preferably synchronously and uniformly adjusting the throws of all of the cams. The throws of the cams can advantageously be adjusted while the knitting machine is operating, to change the takedown rate in coordination with knitting changes.
In accordance with one aspect, the takedown unit of the present invention may reduce the amount of tension imparted on the fabric for takedown, thus allowing the fabric to be drawn down from the knitting cylinder with a minimum force and pressure on the fabric, so that the knitting assembly can knit xe2x80x9cnaturally.xe2x80x9d Also, preferably the tension in the fabric that results from the operation of the takedown unit is not excessive, and is substantially similar in all portions of the knitted fabric being formed, to advantageously provide a uniform knitted fabric. This advantageously seeks to avoid or minimize the introduction of defects and distortion in the knitted fabric, such as pinching or marking of fabrics made with fragile polymer fibers such as polypropylene or yarns with spandex lycra. The present invention also seeks to avoid the introduction of xe2x80x9ctiger stripexe2x80x9d defects in pile fabric, which can be caused by indiscriminate slippage and can result in an undesired appearance after a finish is applied to the fabric. The present invention preferably advantageously keeps the fabric tube from contacting the inside of the needle cylinder, which can be caused by the flattening and thus widening of the fabric tube in conventional takedown units with only two pinch rolls. The present invention also seeks to avoid the introduction of pinched points, slippage marks and fold defects caused by the use of pinch takedown rollers and the pressure between the pinch takedown rollers as the fabric passes through them. The advantages of the present invention also include the possibility of using less power than a traditional takedown unit. It is also expected that the takedown unit of the present invention may be less expensive than prior pinched-type takedown units by eliminating the magnetic takedown clutch and the big ring gear that drives the traditional pinch rolls.
Other aspects and advantages of the present invention will become apparent from the following.